In the past key actuated, electrically controlled mechanisms have included electrically coded keys, key receivers having code sensor circuits, and control circuitry responsive to proper code detection for outputting a control signal to switches controlling the operation of locks, ignition circuits and the like. One art system includes a coded key which when properly inserted in a key receiver type switch will be effective to unlock the system only if the appropriate key has been inserted. The key receiver switch has a code sensor circuit which senses the correct positioning of the key and the key code. The code is decoded in a decoder for comparison with a preset code in a comparator. If the codes match the comparator outputs a signal to a logic control circuit. The presence of the signal and a correct key position indicating signal enables the logic circuit to produce a control signal for an electrically actuated locking mechanism. Those persons desiring additional information for this prior art device are referred to U.S. Pat. No. 4,274,080 issued June 16, 1981 to Brunken.
A similar device is disclosed for burglar proofing vehicles and is disclosed in U.S. Pat. No. 4,347,545 issued Aug. 31, 1982 to Weishaupt et al. and assigned to Bayerische Motoren Werke A.G. (BMW).
Several types of coded keys have been used including magnetically coded keys, electro-optically coded keys, electrically coded keys, and a combination of electrically and mechanically coded keys. Such keys are the subject matter of U.S. Pat. Nos. 4,274,000; 3,870,895; 3,660,624; and 4,686,358.
Disadvantages attending the prior art devices are their failure to prevent known methods of bypassing the protective system using techniques including removal of the device during maintenance for copying, bypassing the mechanism by "hot wiring", or using auxiliary battery placement, for example.
The security system of the present invention is particularly suited for use in coded key ignition systems using any of the known coded key structures. Features which distinguish the present invention over the known prior art include: a structure suitable for use in connection with either electrically or mechanically coded keys; control lines having high current switching capability for driving directly the solenoids of solenoid operated devices; a sequentially driven control circuitry for ensuring that a proper sequence of events occur in the key receiver switch before final device actuation; an electrical identifier signal producer operable in response only to a key operation sequence for allowing the flow of current in a circuit path vital to system operation; and a code storage means which is configurable using either electrical or electronic means.